Electric fence charger



July 27, 1954 H. B. SAUNDERS ELECTRIC FENCE CHARGER Filed Oct. 25, 1952 fi /e gig 5mm. 78M L W M wi u 1 .3 u a n .z u

Patented July 27, 1954 UNITED STATES PATENT OFFICE ELECTRIC FENCE CHARGER Henry B. Saunders, Warrenville, 111., assignor to Grand Sheet Metal Products 00., Melrose Park, 111., a corporation of Illinois Application October 25, 1952, Serial No. 316,865

12 Claims. I

This invention relates to an electric fence charger for use in impressing a high potential at short intervals upon a fence or other barrier to train cattle to remain away therefrom. Such devices are well known and provide a potential of several thousand volts for a short instant of time at periodic intervals. The current normally provided by such charger is too small to kill a human being, although the shock is sufiicient to generate an immediate nervous response.

Conventional fence chargers are frequently designed so that either battery or power line energization is possible. Such chargers usually have a step-up transformer whose secondary feeds high potential of the order of several thousand volts to the load, such as a fence. A balance wheel operated contact mechanism, operated from the leakage flux of the step-up transformer, is provided for interrupting the primary circuit. When energized by a battery, the primary of the step-up transformer is energized and no undue power is impressed upon the load. The balance wheel operated switch is usually on for about .1 second and off for about 1 or 2 seconds.

Upon power line energization, a number of undesired possibilities may exist. Usually, such chargers have a step-down transformer for changing line potential to a low value for energizing the aforementioned step-up transformer. The balance wheel operated switch is still necessary for the purpose of impressing a short pulse on the fence at relatively long intervals of time. During battery operation, the balance wheel operated switch was necessary for transformer action, apart from the pulse action on the load. In such chargers, a low resistance load or a short may cause the balance wheel operated contacts to freeze. When this condition exists, a continuous high potential is impressed upon the fence or load. This creates a very dangerous condition.

Additionally, the power line, which has one side grounded, may have its high side accidentally grounded to the unit or load and create a hazard.

This invention provides a charger construction which renders hazards of the above character impossible. In particular, a construction embodying the present invention makes for a safe unit under all conditions of energization. When battery operated, the power leads are dead and vice versa. Furthermore, when energized from a power line, dangerous power levels either at the unit or load are rendered impossible. In the event of contact freezing, power is automatically cut-off.

A charger embodying the present invention is characterized by electrical simplicity and economy. In particular, the new charger does not require a step-down transformer for power line operation.

The use of a res stor to cut down potential instead of a step-down transformer is well known. In the new charger, a resistance line cord is used to replace a step-down transformer. This resistance line cord, however, also functions as a fuse to disconnect the power line when excessive current is drawn by the charger.

I have found that a resistance line cord by itself will not function satisfactorily in a fence charger having a conventional step-up transformer. In such a charger, a dangerous condition is likely to be created if the load resistance drops to a relatively low value. Thus in the usual chargers, a load resistance of less than about 10,000 ohms may cause contact freezing of the balance wheel operated switch. I have found that a half wave rectifier shunted across the primary of the step-up transformer reduces contact freezing generally to the vanishing point. Such a rectifier may be used with a conventional charger having a step-down transformer for power line energization. The rectifier is essential when a resistance line cord is used to replace a step-down transformer and where the step-up transformer secondary circuit may have a relatively low resistance under certain conditions. If the load circuit of a charger could be maintained at 10,000 ohms or higher under all possible conditions, then the rectifier would not be essential.

The polarity of the rectifier is not important. The rectifier itself may be of the selenium type or any other dry type or of the electron discharge type. The latter type however is rarely used in practical fence chargers and the preferred rectifier is the dry type.

In general, the new and improved fence charger has resistance wire in the power line leads to the charger, said resistance wire being preferably formed of fusible material so that not only Will the current drawn by the charger be limited by virtue of the resistance drop in the leads, but also the charger itself may be disconnected from the power line in the event that an excessive amount of current is drawn by the charger. Other and additional features of the new and improved fence charger will be apparent to those skilled in the art after the same has been explained.

Referring therefore to the drawings:

Figure 1 shows a diagrammatic representation of an exemplary embodiment of a fence charger embodying the present invention, it being understood, however, that this showing is merely illustrative and that variations may be made without departing from the spirit of the invention;

Figure 2 is a bottom view of a fence charger embodying the present invention illustrating the manner in which the high tension output leads are taken from the charger;

Figure 3 shows a circuit diagram of a modification.

The fence charger, as a whole, is housed preferably in a metal cabinet generally indicated by numeral ID. This metal cabinet is preferably sealed to prevent tampering with the interior thereof. Within the cabinet there is step-up transformer 12 having primary l3 and secondary Hi. This transformer has a high leakage reactance and preferably provides a high voltage stepup ratio. It is widely used in the fence charger art.

Secondary [4 has its ends connected to output 7 leads and i6, these leads consisting of high tension insulated cable, such as used in the leads from the distributor to the spark plugs of a accordingly I have provided high tension cable from the transformer through the casing to the outside, such cable usually being several feet long. As is clearly indicated in the drawing, neither side of the high tension terminals of the secondary is connected to the casing.

Transformer primary l3 has terminals i9 and 20. Terminal I9 is connected by wire 2| to movable switch contact 22 of a switch generally indicated by numeral 23. Switch 23 is provided for changing the circuits when the fence charger is to be energized from a battery or from an alternating current power line. Movable contact 22 of switch 23 normally cooperates with fixed contacts 25 and 26, the movable contact touching either one or the other. Switch 23 has movable contact 21 which cooperates with fixed contacts 28 and 29. Fixed contacts 26 and 29 are connected preferably to battery leads 313 and 3!. These leads are lengths of insulated wire passing through the case. In practice, battery leads 30 and 3! may be several feet in length so that they may be connected to a battery when desired.

, ing rather easily upon a predetermined overload in a manner resembling a fuse. Thus line cord 33 functions not only as a permanent resistance during normal operation but also functions as a fuse to prevent dangerous overloads. The cord used is available on the market. Thus for conventional fence chargers, a line cord having a resistance of between about and 20 ohms on each side of the line is ample for most purposes. In some instances, the resistance may be larger or smaller.

Switch 23 has a third movable contact 38 cooperating with fixed contacts 39 and 40. Contact 38 is connected to terminal 28 of the primary. Contact 40 is dead while contact 39 is connected through rectifier 42 back to terminal I9 of the transformer primary. The polarity of rectifier 42 is not important.

Terminal 20 is connected through contacts 44 and 45 to wire 43 going to movable contact 21. Contacts 44 and 45 are part of balance wheel operated mechanism generally indicated by numeral 41 and operated by the leakage flux from transformer [2. The balance wheel operated mechanism is well known and generally consists of a balance wheel and coil spring controlling contacts 44 and 45. In the normal rest position of the balance wheel, contacts 44 and 45 are closed. The balance wheel is generally provided with an armature adapted to be attracted by a part of the transformer core, the balance wheel being given an impulse moving the same away from a contact closing position to a contact opening position.

Between terminal 20 and wire 43 there is connected condenser 49, the same being preferably of sufficient capacitance to prevent arcing at the balance wheel operated contacts. In practice, a capacitance of the order of about one-half a microfarad has been found to be suitable. Condensers having a higher or lower capacitance may be used.

As is clearly indicated in Figure 1, all the mechanism within casing I0 is electrically isolated from the casing. In practice, the charger system may be grounded to the core of transformer l2. As shown in Figure 2, the casing has no binding posts or terminals secured to the casing. Thus all wires coming from within the casing pass through suitable rubber grommets in the casing wall or may be tightly clamped by conventional means.

Switch 23 is shown in battery-operating position in which position, the operating circuit is conventional. When switch 23 is moved to the left, as seen in Figure 1, operation from an alternating current power line is possible. In that position, currents will be impressed upon wires 2! and 43. When the balance wheel operated contacts are closed, as shown, a through circuit for one part of a cycle in one direction is established for current through primary [3. Conventional fence charger action will result on this half wave portion of the cycle. During the other part of the cycle, rectifier 42 will by-pass most of the current. The resistance in the line cord will limit the current on the half cycles both when the rectifier conducts and when the transformer operates.

In all switch positions, unused power leads from the battery or line cord, as the case may be, are completely isolated and dead. Thus no accidental grounds or shorts from idle leads are possible.

The balance wheel operated mechanism operates relatively slowly so that one or more cycles from a conventional 60 cycle power line may flow through the charger While the contacts are closed. When the balance wheel operated contacts are open, condenser 49 will prevent arcing at these balance wheel operated contacts and will also cut the amount of alternating current passing either through primary 13 or through the rectifier, depending upon the part of the cycle considered. In either event, as long as contacts 44 and 45 are open, condenser 49 will have sufiicient reactance so that the current through primary I3 is greatly reduced from the value required to produce a high potential in the secondary.

It is clear that no dangerous potentials or currents can be present in the charger or can be supplied by the charger embodying the present invention.

As previously pointed out, if the secondary circuit resistance can be maintained, at all times and under all possible conditions of power line energization, at about 10,000 ohms or more, the rectifier may be omitted and the resistance line cord used alone.

Referring to Figure 3, a modification is shown where the rectifier across the primary is omitted. Secondary I4 has one terminal connected to output lead 15' while the other terminal is connected to fixed contact 50 and, through resistor 51, to fixed contact 52. Movable contact 53 of switch 23' is connected to the other high voltage output lead 16'. lhe remainder of the system is connected, as in Figure 1.

It is evident that in the modification shown in Figure 3, when the switrh is on battery energization, secondary I4 is connected directly to output leads l5 and it. When the switch is on power line energization, the transformer output is fed through resistor 5|. This resistor may have a value of about 10,000 ohms. Resistor 51 represents a minimum load and prevents sticking of the balance wheel operated contacts. This makes it possible to use a resistance type line cord between the charger and the power line without a rectifier across the primary.

In all cases, the power line potential on the line cord will be very low compared to the output potential across the secondary of the transformer and in practice will usually be about 110 volts or other potential used for domestic consumption. The potential across the transformer primary will always be less than the line voltage.

What is claimed is:

1. A fence charger comprising a casing having a step-up transformer with primary and secondary windings therein, leads from the secondary for connection to a. fence for charging the same, electromagnetic means in said casing for periodicall interrupting the primary circuit, leads for supplying electric power to said primary, said leads consisting of resistance wire extending through a wall of said casing for connection to a grounded alternating current power line, said resistance wire limiting the current intake to the transformer primary to a safe value in the event of an accidental short circuit or ground in the fence charger system, a condenser in series with said primary and a dry type of rectifier connected across the primary.

2. The charger according to claim 1 wherein said casing is of metal and wherein the leads from the secondary comprise high tension insulated cables passing through the casing, and having free ends for connection to the load.

3. A fence charger comprising a casing having a step-up transformer and balance wheel type switch mechanism therein, said transformer having primary and secondary windings, said secondar windings being adapted to supply a high potential for charging a fence or the like, said balance wheel operated mechanism being of the type operating from leakage flux in the transformer and including a pair of normally closed contacts which are opened when current flows through the primary, power leads connected to the primary and balance wheel operated contacts in series, said leads being adapted to be supplied with alternating current from a power source, a condenser connected across the balance wheel operated contacts and a rectifier connected across the transformer primary.

4. The charger according to claim 3 wherein said leads include resistance wire for controlling the amount of current passing through the primary and rectifier.

5. The system according to claim 3 wherein said secondary has high tension cables connected to the terminals thereof and passing through the casing for connection to a load.

6. A fence charger comprising a metal casing having a transformer and balance wheel operated switch therein, said transformer having a primary and secondary adapted to step-up the primary potential to a high secondary potential, said balance wheel operated switch having normally closed contacts which are opened when the balance wheel is attracted by leakage flux from the transformer, said balance wheel operated contacts being connected in series with the primary, a condenser connected across said balance wheel operated contacts, a rectifier connected across the primary only, a pair of power leads connected across the primary and balance wheel operated contacts in series, said pair of leads including fusible resistance wire in each lead thereof for limiting the current to be supplied from a grounded alternating current power line and means for supplying the high potential generated by the secondary to a fence or other load, said casing being of metal and being normally disconnected to the charger or any parts thereof.

7. The charger according to claim 6 wherein said secondary has high tension cables connected to the terminals within the casing, said cables passing through the casing and having free lengths for connection to a load.

8. The charger according to claim 6 wherein a pair of battery leads is provided, a three pole double throw switch, said switch having battery and power line energization positions respectively, connections between said battery leads, power leads and switch for cutting out the rectifier and substituting the battery leads for the power leads in the battery energization switch position, said switch isolating the battery leads in the power line energization position.

9. A fence charger comprising a metal casing having a transformer and balance wheel operated switch therein, said transformer having a primary and secondary adapted to step-up the primary potential to a high secondary potential, said balance wheel operated switch having normally closed contacts which are opened when the balance wheel is attracted by leakage flux from th transformer, said balance wheel operated contacts being connected in series with the primary, a condenser connected across said balance wheel operated contacts, a pair of power leads connected across the primary and balance wheel operated contacts in series, said pair of leads including fusible resistance wire in each lead thereof for limiting the current to be supplied from a grounded alternating current power line, said secondary having connections for supplying secondary potential to a fence to be charged, said connections including a resistor having substantial value so that for power line energization, current to the primary goes through the fusible resistance wires and current in the secondary g0es through the last named resistor in the secondary connections.

7 10. The charger according to claim 9 wherein said resistor has a value of about 10,000 ohms.

1'1. The charger according to claim 9 wherein battery leads are provided, switch means for connecting either the power line leads or the battery the transformer, said balance wheel operated contacts being connected in series with the primary, a condenser connected across said balance wheel operated contacts, said secondary having connections for supplying secondary potential to a fence to be charged, said connections including a resistor of the order of about 10,000 ohms, said resistor serving to limit the loading of the secondary winding to a minimum value equal to the resistance of the resistor to insure substantially satisfactory operation of the charger under all fence conditions.

References Cited in the file of this patent UNITED STATES PATENTS Name Date Roberts June 2'7, 1950 Number 

